Acoustic Wave Filter and Multiplexer

This application claims the benefit of priority to Japanese Patent Application No. 2024-171932 filed on Oct. 1, 2024. The entire contents of this application are hereby incorporated herein by reference.

The present invention relates to acoustic wave filters and multiplexers.

To date, acoustic wave filters have been used widely as filters in cellular phones. International Publication No. 2019/131533 discloses an example of an acoustic wave filter. The acoustic wave filter has a longitudinally coupled resonator unit. The longitudinally coupled resonator unit includes three or more interdigital transducer (IDT) electrodes. Each IDT electrode includes a pair of comb-shaped electrodes. One of the comb-shaped electrodes in each IDT electrode is connected to the signal potential, the other is connected to the ground potential. Comb-shaped electrodes of some of the IDT electrodes are connected to the ground potential through the same wiring line. Comb-shaped electrodes of the remaining IDT electrodes are connected to the ground potential through a wiring line different from the wiring line described above.

For example, the acoustic wave filter described in International Publication No. 2019/131533 is used along with other filter devices in a multiplexer such as a duplexer. However, the acoustic wave filter has a difficulty in making the out-of-band attenuation sufficiently high. Therefore, when the acoustic wave filter is used in a multiplexer, it is difficult to make the isolation characteristics sufficiently high.

Example embodiments of the present invention provide acoustic wave filters each with a larger out-of-band attenuation, and multiplexers each with improved isolation characteristics.

An acoustic wave filter according to an example embodiment of the present invention includes a longitudinally coupled resonator acoustic wave filter including n IDT electrodes where n is an odd number of seven or more, and a first reference-potential wiring line and a second reference-potential wiring line each connected to a reference potential. The longitudinally coupled resonator acoustic wave filter includes a first area and a second area. The first area includes a first-end-positioned IDT electrode to a center-positioned IDT electrode in a direction in which the n IDT electrodes are arranged side by side. The second area includes the center-positioned IDT electrode to a second-end-positioned IDT electrode in the direction in which the n IDT electrodes are arranged side by side. Each of the IDT electrodes includes a first comb-shaped electrode and a second comb-shaped electrode interdigitated with each other. One of the first comb-shaped electrode and the second comb-shaped electrode in each IDT electrode is connected to a signal potential. An other of the first comb-shaped electrode and the second comb-shaped electrode is connected to the reference potential. A first one in each pair of adjacent IDT electrodes includes the first comb-shaped electrode connected to the signal potential. A second one in the pair includes the first comb-shaped electrode connected to the reference potential. In the first area, all of the first comb-shaped electrodes connected to the reference potential are connected to the first reference-potential wiring line, and the second comb-shaped electrodes connected to the reference potential include a second comb-shaped electrode connected to the first reference-potential wiring line and a second comb-shaped electrode connected to the second reference-potential wiring line. In the second area, the first comb-shaped electrodes connected to the reference potential include a first comb-shaped electrode connected to the first reference-potential wiring line and a first comb-shaped electrode connected to the second reference-potential wiring line, and all of the second comb-shaped electrodes connected to the reference potential are connected to the second reference-potential wiring line.

A multiplexer according to an example embodiment of the present invention includes multiple filter devices. At least one of the filter devices includes an acoustic wave filter according to an example embodiment of the present invention.

Acoustic wave filters according to example embodiments of the present invention each achieve a larger out-of-band attenuation. Multiplexers according to example embodiments of the present invention each achieve improved isolation characteristics.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings.

Referring to the drawings, example embodiments of the present invention will be described in detail.

Example embodiments of the present invention described in this specification are examples, and partial replacement or combination of configurations in different example embodiments may be made.

1 FIG. is a circuit diagram of a duplexer according to a first example embodiment of the present invention.

10 10 1 1 2 1 1 2 1 A duplexeris a multiplexer according to the first example embodiment of the present invention. Specifically, the duplexerincludes a receive filterA, a transmit filterB, and a common connection terminal. The receive filterA and the transmit filterB are commonly connected to the common connection terminal. The receive filterA is an acoustic wave filter according to an example embodiment of the present invention.

The multiplexer according to an example embodiment of the present invention is not limited to a duplexer. For example, the multiplexer may include three or more filter devices. Any configuration may be provided as long as at least one of the filter devices included in the multiplexer is an acoustic wave filter according to an example embodiment of the present invention.

10 1 1 1 1 In the specification, the passband of the multiplexer or the filter devices is a band defined by a standard for a communication band or the like. The communication band of the duplexeris, for example, Band 28. Thus, the passband of the receive filterA is, for example, about 758 MHz to about 803 MHz which defines and functions as the receive band of Band 28. The passband of the transmit filterB is, for example, about 703 MHz to about 748 MHz which defines and functions as the transmit band of Band 28. The passbands of the receive filterA and the transmit filterB are not limited to those described above.

1 FIG. 1 3 4 4 9 9 12 12 As illustrated in, the receive filterA includes a longitudinally coupled resonator acoustic wave filter, multiple acoustic wave resonators, a first signal terminalA, a second signal terminalB, a first reference-potential wiring lineA and a second reference-potential wiring lineB, a first reference-potential terminalA, and a second reference-potential terminalB. Specifically, the acoustic wave resonators include multiple serial arm resonators and multiple parallel arm resonators.

9 9 12 12 9 12 9 12 9 12 9 12 Each of the first reference-potential wiring lineA and the second reference-potential wiring lineB is a wiring line connected to the reference potential. Each of the first reference-potential terminalA and the second reference-potential terminalB is a terminal connected to the reference potential. The first reference-potential wiring lineA is connected to the first reference-potential terminalA. Thus, the first reference-potential wiring lineA is connected to the reference potential through the first reference-potential terminalA. The second reference-potential wiring lineB is connected to the second reference-potential terminalB. Thus, the second reference-potential wiring lineB is connected to the reference potential through the second reference-potential terminalB.

1 1 4 4 In contrast, the transmit filterB is, for example, a ladder filter. Specifically, the transmit filterB includes multiple serial arm resonators and multiple parallel arm resonators, a third signal terminalC, and a fourth signal terminalD. In the description below, the acoustic wave resonators, the serial arm resonators, the parallel arm resonators, and the longitudinally coupled resonator acoustic wave filter may be described collectively as resonators.

4 1 4 1 2 2 2 The first signal terminalA of the receive filterA and the fourth signal terminalD of the transmit filterB are connected to the common connection terminal. The common connection terminalis, for example, an antenna terminal. The antenna terminal is connected to an antenna. The common connection terminalis not necessarily an antenna terminal.

2 4 4 12 12 4 4 In the present example embodiment, the common connection terminal, the second signal terminalB, the third signal terminalC, the first reference-potential terminalA, and the second reference-potential terminalB are defined by electrode pads. In contrast, the first signal terminalA and the fourth signal terminalD are defined by wiring lines. Each of the terminals may be defined by an electrode pad or a wiring line.

1 3 4 4 3 In the receive filterA, the longitudinally coupled resonator acoustic wave filteris connected between the first signal terminalA and the second signal terminalB. A specific configuration of the longitudinally coupled resonator acoustic wave filterwill be described below.

2 FIG. 2 FIG. 2 FIG. 9 9 is a schematic plan view of a longitudinally coupled resonator acoustic wave filter according to the first example embodiment.illustrates the first reference-potential wiring lineA by using a long dashed short dashed line, and illustrates the second reference-potential wiring lineB by using a dashed line.illustrates areas, described below, by using a dashed line and a long dashed double-short dashed line. The same is true for schematic views, described below, of the longitudinally coupled resonator acoustic wave filter.

3 5 10 5 3 5 5 5 The longitudinally coupled resonator acoustic wave filterincludes a piezoelectric substrateand multiple interdigital transducer (IDT) electrodes. The duplexermay include the piezoelectric substrateincluding the longitudinally coupled resonator acoustic wave filter. The piezoelectric substratehas piezoelectricity. The piezoelectric substrateincludes only piezoelectric material. The piezoelectric material may be, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, crystal, or lead zirconate titanate (PZT). The piezoelectric substratemay be a multilayer substrate including a piezoelectric layer.

1 1 5 5 2 4 4 4 4 12 12 5 5 5 1 FIG. 1 FIG. In the present example embodiment, all of the resonators of the receive filterA and the transmit filterB inshare the piezoelectric substrate. The terminals inare disposed on the piezoelectric substrate. More specifically, the common connection terminal, the first signal terminalA, the second signal terminalB, the third signal terminalC, the fourth signal terminalD, the first reference-potential terminalA, and the second reference-potential terminalB are disposed on the piezoelectric substrate. However, each resonator may include its own piezoelectric substrate. Multiple terminals may be provided on piezoelectric substratesdifferent from each other.

2 FIG. 3 5 3 6 6 6 6 6 6 6 6 6 3 As illustrated in, the longitudinally coupled resonator acoustic wave filterincludes, for example, nine IDT electrodes. The nine IDT electrodes are disposed on the piezoelectric substrate. Specifically, the nine IDT electrodes of the longitudinally coupled resonator acoustic wave filterinclude an IDT electrodeA, an IDT electrodeB, an IDT electrodeC, an IDT electrodeD, an IDT electrodeE, an IDT electrodeF, an IDT electrodeG, an IDT electrodeH, and an IDT electrodeI. The longitudinally coupled resonator acoustic wave filterhas a one-stage configuration.

3 3 The number of IDT electrodes of the longitudinally coupled resonator acoustic wave filteris not limited to nine. In example embodiments of the present invention, any configuration may be provided as long as the longitudinally coupled resonator acoustic wave filterincludes n IDT electrodes where n is an odd number of seven or more. More specifically, in example embodiments of the present invention, n is any odd number of seven or more, and, for example, n=9 in the first example embodiment. However, in example embodiments of the present invention, n may be an odd number, such as seven or eleven, for example.

6 3 7 7 7 16 18 18 16 7 17 19 19 17 The IDT electrodeA of the longitudinally coupled resonator acoustic wave filterincludes a pair of comb-shaped electrodes. Specifically, the pair of comb-shaped electrodes include a first comb-shaped electrodeA and a second comb-shaped electrodeB. The first comb-shaped electrodeA includes a first busbarand multiple first electrode fingers. One end of each of the first electrode fingersis connected to the first busbar. The second comb-shaped electrodeB includes a second busbarand multiple second electrode fingers. One end of each of the second electrode fingersis connected to the second busbar.

7 7 16 17 18 19 7 7 The first comb-shaped electrodeA and the second comb-shaped electrodeB are arranged so that the first busbaris opposite the second busbar. The first electrode fingersand the second electrode fingersare interdigitated with each other. Thus, the first comb-shaped electrodeA and the second comb-shaped electrodeB are interdigitated with each other.

7 7 18 19 16 17 In the description below, the first comb-shaped electrodeA and the second comb-shaped electrodeB may be collectively described simply as comb-shaped electrodes. The first electrode fingersand the second electrode fingersmay be collectively described simply as electrode fingers. The direction in which the electrode fingers extend is referred to as the electrode-finger extension direction, the direction orthogonal or substantially orthogonal to the electrode-finger extension direction is referred to as the electrode-finger orthogonal direction. The first busbaris positioned on one side in the electrode-finger extension direction, and the second busbaris positioned on the other side.

6 6 3 3 Similar to the IDT electrodeA, each of the IDT electrodes other than the IDT electrodeA of the longitudinally coupled resonator acoustic wave filterincludes a pair of comb-shaped electrodes. The electrode-finger orthogonal direction of each IDT electrode of the longitudinally coupled resonator acoustic wave filteris the same.

3 6 6 6 6 6 6 6 6 6 Application of an alternating voltage to each IDT electrode causes acoustic waves to be excited. The acoustic-wave propagation direction of each IDT electrode is parallel or substantially parallel to the electrode-finger orthogonal direction. The nine IDT electrodes of the longitudinally coupled resonator acoustic wave filterare arranged side by side in the acoustic-wave propagation direction. Specifically, in the direction in which the nine IDT electrodes are arranged side by side, the IDT electrodeA, the IDT electrodeB, the IDT electrodeC, the IDT electrodeD, the IDT the electrodeE, the IDT electrodeF, the IDT electrodeG, the IDT electrodeH, and the IDT electrodeI are arranged side by side in this order.

3 8 8 8 8 5 The longitudinally coupled resonator acoustic wave filterincludes a pair of reflectors. Specifically, the pair of reflectors include a reflectorA and a reflectorB. More specifically, the reflectorA and the reflectorB are arranged on the piezoelectric substrateso as to be opposite each other with the nine IDT electrodes interposed in between in the acoustic-wave propagation direction. Each of the IDT electrodes and the reflectors may include a multilayer metal film or a single-layer metal film.

3 FIG. 3 FIG. 3 FIG. 3 FIG. 3 FIG. 3 FIG. 3 FIG. 3 FIG. is a schematic view of the longitudinally coupled resonator acoustic wave filter according to the first example embodiment. In, each of the IDT electrodes and the reflectors is illustrated as a rectangular schematic figure. In, each of the IDT electrodes is hatched. In, wiring lines connected to upper portions, in, of IDT electrodes indicate that the wiring lines are connected to the first comb-shaped electrodes of the IDT electrodes. In contrast, in, wiring lines connected to lower portions, in, of IDT electrodes indicate that the wiring lines are connected to the second comb-shaped electrodes of the IDT electrodes. The same is true in schematic views other than that in.

6 6 6 6 6 6 6 6 6 6 In the description below, the order in which the nine IDT electrodes are arranged side by side represents the numbers of the IDT electrodes, and the number of the IDT electrodeA is one. The numbers of the IDT electrodeA, the IDT electrodeC, the IDT electrodeE, the IDT electrodeG, and the IDT electrodeI are odd. In contrast, the numbers of the IDT electrodeB, the IDT electrodeD, the IDT electrodeF, and the IDT electrodeH are even.

6 4 In each IDT electrode, the first comb-shaped electrode or the second comb-shaped electrode is connected to the signal potential, and the other of the first comb-shaped electrode or the second comb-shaped electrode is connected to the reference potential. Specifically, in the first IDT electrodeA, the first comb-shaped electrode is connected to the reference potential, and the second comb-shaped electrode is connected to the signal potential. In each of the other odd-numbered IDT electrodes, the first comb-shaped electrode is connected to the reference potential, and the second comb-shaped electrode is connected to the signal potential. More specifically, the second comb-shaped electrodes in the odd-numbered IDT electrode are connected to the signal potential on the second signal terminalB side.

4 In contrast, in each even-numbered IDT electrode, the first comb-shaped electrode is connected to the signal potential, and the second comb-shaped electrode is connected to the reference potential. More specifically, the first comb-shaped electrodes in the even-numbered IDT electrode are connected to the signal potential on the first signal terminalA side.

3 In the longitudinally coupled resonator acoustic wave filter, any of the odd-numbered IDT electrodes is adjacent to any of the even-numbered IDT electrodes. The first comb-shaped electrode of one of the adjacent IDT electrodes is connected to the signal potential, and the first comb-shaped electrode of the other of the adjacent IDT electrodes is connected to the reference potential.

5 9 9 9 9 3 9 9 On the piezoelectric substrate, the first reference-potential wiring lineA, which is schematically illustrated by using a long dashed short dashed line, and the second reference-potential wiring lineB, which is schematically illustrated by using a dashed line, are provided. The first reference-potential wiring lineA and the second reference-potential wiring lineB are connected to the reference potential. In the longitudinally coupled resonator acoustic wave filter, the comb-shaped electrodes connected to the reference potential are connected to the first reference-potential wiring lineA or the second reference-potential wiring lineB.

9 9 12 12 1 9 9 The first reference-potential wiring lineA is not connected to the second reference-potential wiring lineB. The first reference-potential terminalA is not connected to the second reference-potential terminalB. That is, in the receive filterA defining and functioning as an acoustic wave filter, the path on which the first reference-potential wiring lineA is connected to the reference potential is different from the path on which the second reference-potential wiring lineB is connected to the reference potential.

3 FIG. 3 6 6 6 6 As illustrated in, the longitudinally coupled resonator acoustic wave filterincludes a first area A and a second area B. Specifically, the first area A is an area including the IDT electrodeA, which is positioned at one end, to the IDT electrodeE, which is positioned at the center, in the direction in which the nine IDT electrodes are arranged side by side. The second area B is an area including the IDT electrodeE, which is positioned at the center, to the IDT electrodeI, which is positioned on the other end, in the direction in which the nine IDT electrodes are arranged side by side.

6 6 6 9 In the first area A, the first comb-shaped electrodes connected to the reference potential are those of the IDT electrodeA, the IDT electrodeC, and the IDT electrodeE. All of these first comb-shaped electrodes are connected to the first reference-potential wiring lineA.

6 6 6 9 6 9 9 9 In the first area A, the second comb-shaped electrodes connected to the reference potential are those of the IDT electrodeB and the IDT electrodeD. The second comb-shaped electrode of the IDT electrodeB is connected to the first reference-potential wiring lineA. The second comb-shaped electrode of the IDT electrodeD is connected to the second reference-potential wiring lineB. Thus, the second comb-shaped electrodes connected to the reference potential include a second comb-shaped electrode connected to the first reference-potential wiring lineA and a second comb-shaped electrode connected to the second reference-potential wiring lineB.

6 6 6 6 6 9 6 9 9 9 In the second area B, the first comb-shaped electrodes connected to the reference potential are those of the IDT electrodeE, the IDT electrodeG, and the IDT electrodeI. The first comb-shaped electrodes of the IDT electrodeE and the IDT electrodeG are connected to the first reference-potential wiring lineA. The first comb-shaped electrode of the IDT electrodeI is connected to the second reference-potential wiring lineB. Thus, the first comb-shaped electrodes connected to the reference potential include a first comb-shaped electrode connected to the first reference-potential wiring lineA and a first comb-shaped electrode connected to the second reference-potential wiring lineB.

6 6 9 In the second area B, the second comb-shaped electrodes connected to the reference potential are those of the IDT electrodeF and the IDT electrodeH. All of these second comb-shaped electrodes are connected to the second reference-potential wiring lineB.

9 9 9 9 9 9 The present example embodiment includes the following four configurations 1) to 4). 1) In the first area A, all of the first comb-shaped electrodes connected to the reference potential are connected to the first reference-potential wiring lineA. 2) In the first area A, the second comb-shaped electrodes connected to the reference potential include a second comb-shaped electrode connected to the first reference-potential wiring lineA and a second comb-shaped electrode connected to the second reference-potential wiring lineB. 3) In the second area B, the first comb-shaped electrodes connected to the reference potential include a first comb-shaped electrode connected to the first reference-potential wiring lineA and a first comb-shaped electrode connected to the second reference-potential wiring lineB. 4) In the second area B, all of the second comb-shaped electrodes connected to the reference potential are connected to the second reference-potential wiring lineB.

3 1 1 10 The longitudinally coupled resonator acoustic wave filter, which includes the configurations 1) to 4) described above, in the receive filterA defining and functioning as an acoustic wave filter achieves an increase of the out-of-band attenuation of the receive filterA. Thus, the duplexerachieves improved isolation characteristics. The details of this will be described below with the details of the circuit configuration in the present example embodiment.

1 FIG. 1 3 4 4 1 2 3 4 4 2 4 1 4 As illustrated in, the receive filterA includes the longitudinally coupled resonator acoustic wave filter, the acoustic wave resonators, the first signal terminalA, the second signal terminalB, an inductor L, and an inductor L. The longitudinally coupled resonator acoustic wave filteris connected between the first signal terminalA and the second signal terminalB. A signal received from the common connection terminalis input to the first signal terminalA, and is output through devices in the receive filterA from the second signal terminalB.

1 1 1 2 3 1 4 3 2 3 3 4 Specifically, the acoustic wave resonators in the receive filterA include multiple serial arm resonators and multiple parallel arm resonators. More specifically, the serial arm resonators in the receive filterA include a serial arm resonator S, a serial arm resonator S, and a serial arm resonator S. The serial arm resonator Sis connected between the first signal terminalA and the longitudinally coupled resonator acoustic wave filter. The serial arm resonator Sand the serial arm resonator Sare connected in series to each other between the longitudinally coupled resonator acoustic wave filterand the second signal terminalB.

1 1 2 1 1 3 2 2 3 1 12 12 1 2 12 12 2 1 2 More specifically, the parallel arm resonators in the receive filterA include a parallel arm resonator Pand a parallel arm resonator P. The parallel arm resonator Pis connected between the reference potential and the connection point between the serial arm resonator Sand the longitudinally coupled resonator acoustic wave filter. The parallel arm resonator Pis connected between the reference potential and the connection point between the serial arm resonator Sand the serial arm resonator S. The parallel arm resonator Pis connected to the first reference-potential terminalA. The first reference-potential terminalA is connected to the inductor L. In contrast, the parallel arm resonator Pis connected to the second reference-potential terminalB. The second reference-potential terminalB is connected to the inductor L. The inductor Land the inductor Lare connected to the reference potential.

1 9 9 1 12 3 1 1 The parallel arm resonator Pis connected to the first reference-potential wiring lineA. The first reference-potential wiring lineA is connected to the inductor Lthrough the first reference-potential terminalA. Thus, among all of the IDT electrodes in the longitudinally coupled resonator acoustic wave filter, comb-shaped electrodes of some of the IDT electrodes and the parallel arm resonator Pare connected in common to the reference potential through the inductor L.

2 9 9 2 12 3 2 2 In contrast, the parallel arm resonator Pis connected to the second reference-potential wiring lineB. The second reference-potential wiring lineB is connected to the inductor Lthrough the second reference-potential terminalB. Thus, among all of the IDT electrodes in the longitudinally coupled resonator acoustic wave filter, comb-shaped electrodes of some of the IDT electrodes and the parallel arm resonator Pare connected in common to the reference potential through the inductor L.

1 1 2 3 9 9 However, the circuit configuration of the receive filterA, which is an acoustic wave filter according to an example embodiment of the present invention is not limited to that described above. For example, the inductor Land the inductor Lare not necessarily provided. An acoustic wave filter according to an example embodiment of the present invention may have any configuration as long as it includes the longitudinally coupled resonator acoustic wave filter, the first reference-potential wiring lineA, and the second reference-potential wiring lineB.

1 4 4 3 4 The transmit filterB includes the serial arm resonators, the parallel arm resonators, the third signal terminalC, the fourth signal terminalD, an inductor L, and an inductor L.

1 11 11 12 12 13 14 4 4 11 11 12 12 13 14 4 a b a b a b a b More specifically, the serial arm resonators of the transmit filterB include a serial arm resonator S, a serial arm resonator S, a serial arm resonator S, a serial arm resonator S, a serial arm resonator S, and a serial arm resonator S. The serial arm resonators are connected in series to each other between the third signal terminalC and the fourth signal terminalD. More specifically, in the circuit configuration, the serial arm resonator S, the serial arm resonator S, the serial arm resonator S, the serial arm resonator S, the serial arm resonator S, and the serial arm resonator Sare provided in this order from the third signal terminalC side.

1 11 12 13 14 11 4 12 11 12 13 12 13 14 13 14 b a b More specifically, the parallel arm resonators of the transmit filterB include a parallel arm resonator P, a parallel arm resonator P, a parallel arm resonator P, and a parallel arm resonator P. The parallel arm resonator Pis connected between the third signal terminalC and the reference potential. The parallel arm resonator Pis connected between the reference potential and the connection point between the serial arm resonator Sand the serial arm resonator S. The parallel arm resonator Pis connected between the reference potential and the connection point between the serial arm resonator Sand the serial arm resonator S. The parallel arm resonator Pis connected between the reference potential and the connection point between the serial arm resonator Sand the serial arm resonator S.

11 12 13 3 14 4 3 4 1 The parallel arm resonator P, the parallel arm resonator P, and the parallel arm resonator Pare connected in common to the inductor L. The parallel arm resonator Pis connected to the inductor L. The inductor Land the inductor Lare connected to the reference potential. However, the circuit configuration of the transmit filterB is not limited to that described above.

10 As described above, the duplexeraccording to the present example embodiment achieves improved isolation characteristics. The details of the advantageous effects will be described below by comparing the present example embodiment with a first comparison example and a second comparison example.

4 FIG. 109 109 109 The circuit configurations of the first comparison example and the second comparison example are different from that according to the first example embodiment only in the receive filter's configuration of wiring lines connecting the longitudinally coupled resonator acoustic wave filter and the parallel arm resonators to the reference potential. As illustrated in, a receive filter according to the first comparison example includes a reference-potential wiring line. The reference-potential wiring lineis connected to the reference potential. The reference-potential wiring lineis connected to all of the comb-shaped electrodes connected to the reference potential.

109 1 2 109 1 2 1 FIG. 4 FIG. The reference-potential wiring lineis connected to both of the parallel arm resonator Pand the parallel arm resonator Pwhich are illustrated in. As illustrated in, the reference-potential wiring lineis connected to the reference potential through both of the inductor Land the inductor L.

5 FIG. 109 109 109 109 109 1 109 2 As illustrated in, a receive filter according to the second comparison example includes a first reference-potential wiring lineA and a second reference-potential wiring lineB. The first reference-potential wiring lineA and the second reference-potential wiring lineB are connected to the reference potential. The first reference-potential wiring lineA is connected to the reference potential through the inductor L. The second reference-potential wiring lineB is connected to the reference potential through the inductor L.

109 109 109 6 109 6 6 6 109 All of the first comb-shaped electrodes connected to the reference potential are connected to the first reference-potential wiring lineA. The second comb-shaped electrodes connected to the reference potential include a second comb-shaped electrode connected to the first reference-potential wiring lineA and a second comb-shaped electrode connected to the second reference-potential wiring lineB. Specifically, the second comb-shaped electrode of the IDT electrodeB is connected to the first reference-potential wiring lineA. The second comb-shaped electrodes of the IDT electrodeD, the IDT electrodeF, and the IDT electrodeH are connected to the second reference-potential wiring lineB.

109 1 109 2 5 FIG. 1 FIG. 5 FIG. 1 FIG. The first reference-potential wiring lineA illustrated inis connected to the parallel arm resonator Pillustrated in. The second reference-potential wiring lineB illustrated inis connected to the parallel arm resonator Pillustrated in.

The isolation characteristics are compared among the first example embodiment, the first comparison example, and the second comparison example. In the first example embodiment, the first comparison example, and the second comparison example, the passband of the transmit filters is about 703 MHz to about 748 MHz, and the passband of the receive filters is about 758 MHz to about 803 MHz, for example.

6 FIG. is a diagram illustrating isolation characteristics of duplexers according to the first example embodiment, the first comparison example, and the second comparison example.

6 FIG. In, as illustrated by using a surrounding long dashed double-short dashed line, it was discovered that the first example embodiment achieves more improved isolation characteristics than those in the first comparison example and the second comparison example.

Specifically, in the first comparison example, the minimum of the absolute value of isolation is about 59.5, which is small, in the passband of the transmit filter. In the second comparison example, the minimum of the absolute value of isolation is about 62.3 in the passband of the transmit filter. The second comparison example achieves more improved isolation characteristics than those in the first comparison example. In contrast, in the first example embodiment, the minimum of the absolute value of isolation is about 63.1, which is large, in the passband of the transmit filter. That is, the first example embodiment achieves further improved isolation characteristics than the second comparison example.

1 1 The attenuation-frequency characteristics of the transmit filterB and the receive filterA in the first example embodiment will be described below. The attenuation-frequency characteristics of the transmit filter and the receive filter according to the second comparison example will be also described below.

7 FIG. 8 FIG. 9 FIG. 8 FIG. 7 9 FIGS.to 7 8 FIGS.and 1 2 is a diagram illustrating attenuation-frequency characteristics of the transmit filters according to the first example embodiment and the second comparison example.is a diagram illustrating attenuation-frequency characteristics of the receive filters according to the first example embodiment and the second comparison example.is an enlarged view of the vicinity of the passband of the transmit filters in. In, the passband of the transmit filters is represented by W. In, the passband of the receive filters is represented by W.

7 FIG. As illustrated in, there is very little difference in the attenuation-frequency characteristics of the transmit filters between the first example embodiment and the second comparison example.

8 9 FIGS.and 1 10 As illustrated in, in the first example embodiment, the out-of-band attenuation of the receive filter is larger than that in the second comparison example. More specifically, in the passband W, the attenuation of the receive filter according to the first example embodiment is larger than that according to the second comparison example. Thus, the duplexeraccording to the first example embodiment may achieve improved isolation characteristics.

In the first example embodiment, an example in which only one filter device in the multiplexer is an acoustic wave filter according to an example embodiment of the present invention is described. However, multiple filter devices in a multiplexer may be acoustic wave filters according to example embodiments of the present invention.

Preferably, at least one filter device in a multiplexer is an acoustic wave filter according to an example embodiment of the present invention, and the passband of the at least one acoustic wave filter is positioned in a higher range than the passband of at least one filter device other than the acoustic wave filter. This may more reliably improve the isolation characteristics of the multiplexer. The state in which a first one of the passbands is positioned on a higher range than a second one of the passbands means that all of the frequencies in the first one of the passbands are higher than all of the frequencies in the second one of the passbands.

1 FIG. 1 9 2 9 1 2 As in the first example embodiment illustrated in, it is preferable that multiple parallel arm resonators include the parallel arm resonator Pconnected to the first reference-potential wiring lineA and the parallel arm resonator Pconnected to the second reference-potential wiring lineB. This makes it possible that the frequency at the attenuation pole contributed by the parallel arm resonator Pis different from that contributed by the parallel arm resonator P. This may achieve a wide range of choices with respect to the frequency range in a band having a large out-of-band attenuation and with respect to adjustment of the magnitude of attenuation in the band.

1 9 9 1 2 1 2 More specifically, in the receive filterA defining and functioning as an acoustic wave filter, the path on which the first reference-potential wiring lineA is connected to the reference potential is different from the path on which the second reference-potential wiring lineB is connected to the reference potential. Therefore, the path on which the parallel arm resonator Pis connected to the reference potential is different from the path on which the parallel arm resonator Pis connected to the reference potential. This causes a state in which, in the attenuation-frequency characteristics of the acoustic wave filter, the frequency at the attenuation pole contributed by the parallel arm resonator Pis different from that contributed by the parallel arm resonator P.

5 1 2 3 4 5 9 9 5 12 12 1 3 FIG. 1 FIG. In the present example embodiment, the piezoelectric substrateillustrated inis mounted in a package substrate (not illustrated) as a chip including the terminals, the wiring lines, and the resonators. The inductor L, the inductor L, the inductor L, and the inductor Lillustrated inare provided in the package substrate. As described above, on the piezoelectric substrate, the first reference-potential wiring lineA is not connected to the second reference-potential wiring lineB. Similarly, on the piezoelectric substrate, the first reference-potential terminalA is not connected to the second reference-potential terminalB. However, the package substrate may include a common path on which the receive filterA defining and functioning as an acoustic wave filter is connected to the reference potential.

1 5 9 1 1 12 9 12 1 9 1 12 For example, the inductor Lmay be provided on the piezoelectric substrate. In this case, for example, the first reference-potential wiring lineA is connected to the inductor L. The inductor Lis connected to the first reference-potential terminalA. That is, the first reference-potential wiring lineA is connected to the first reference-potential terminalA through the inductor L. The first reference-potential wiring lineA is connected to the reference potential through the inductor Land the first reference-potential terminalA.

2 5 9 2 2 12 9 12 2 9 2 12 Similarly, for example, the inductor Lmay be provided on the piezoelectric substrate. In this case, for example, the second reference-potential wiring lineB is connected to the inductor L. The inductor Lis connected to the second reference-potential terminalB. That is, the second reference-potential wiring lineB is connected to the second reference-potential terminalB through the inductor L. The second reference-potential wiring lineB is connected to the reference potential through the inductor Land the second reference-potential terminalB.

10 FIG. is a schematic view of a multiplexer according to a second example embodiment of the present invention.

20 20 1 1 21 1 1 A multiplexeraccording to the present example embodiment includes three or more filter devices. Specifically, the multiplexerincludes the receive filterA, the transmit filterB, a filter deviceC, and at least one different filter device. The receive filterA and the transmit filterB are, for example, the same or substantially the same as those according to the first example embodiment.

21 1 1 21 For example, the filter deviceC may be a receive filter, or may be a transmit filter. The same is true for the filter device other than the receive filterA, the transmit filterB, and the filter deviceC.

20 1 20 The multiplexerincludes the receive filterA defining and functioning as an acoustic wave filter according to an example embodiment of the present invention. As in the first example embodiment, the multiplexerachieves improved isolation characteristics.

20 1 21 The multiplexermay include an acoustic wave filter an example embodiment of the present invention and which is other than the receive filterA. In this case, for example, the passband of the acoustic wave filter is preferably positioned on a higher range than the passband of the filter deviceC or the like. This may more reliably improve isolation characteristics.

While example embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.